This invention generally relates to a device for mixing and dispensing a mixture of fluids and, more particularly, to a device for mixing two reactive fluids in a homogeneous reactive mixture and dispensing the mixture into an open mold.
Conventionally, fluids flowing under pressure are mixed in and ejected from devices such as dispensing guns. In such guns, the fluids are separately introduced into a mixing chamber, having an open outlet end, from spaced inlets opening into the chamber. A plunger, occupying the chamber, exposes the inlets in a rearward position and permits fluids to flow into the chamber, mix, and be ejected from the outlet end. Movement of the plunger toward its forward position closes the inlets and purges the chamber by expelling any residual material therein. The purpose of the plunger is to purge the chamber of any quantities of residual materials, as well as to open and close the inlets communicating with the chamber.
To date, manufacturers of dispensing guns have overlooked the crucial point of having the fluid system completely filled and under uniform fluid pressure before the inlets to the mixing chamber are opened. If the first fluid component arrives at its inlet prior to the other fluid component arriving at its inlet, the first fluid component fills the mixing chamber and crosses over to the other unfilled inlet. One attempt to overcome this problem has been to open valves at the inlets at the same instant the plunger occupying the chamber is retracted therefrom. Other attempts have been made to open valves at the inlets simultaneously, however the inlets may or may not have full fluid components present at the same instant. It has been found that if one or the other of the fluid component's pressure is lost during the standby, the unfilled inlet is again exposed to a possible crossover of fluid from the other inlet. Also, it has been found in practice that reactive fluids tend to seep around the plunger in the closed position, mix, and react to indeed subsequent operation of the dispensing gun.
In U.S. Pat. No. 4,471,887, there is disclosed a dispensing gun which is provided with spring-biased, normally closed check valves at each of the reactive fluid inlets to the mixing chamber. The check valves are opened by the pressure of the reactive fluid components. Each fluid passage supplying a reactive fluid component to the check valves is provided with an on-off valve adapted to be opened and closed in conjunction with the reciprocating movement of a plunger in the mixing chamber.